The present invention relates to a phased-array antenna apparatus which is used in a microwave or milliwave band to change the feeding phases for radiating elements by using digital phase shifters.
A phased-array antenna apparatus is an antenna which scans a radiant beam by electronically changing the feeding phases for a plurality of radiating elements. Phase shifters are respectively connected to the radiating elements. The feeding phases for the radiating elements can be changed by controlling the phase shifters.
In general, a digital phase shifter with 3 to 5 bits (to be simply referred to as a digital phase shifter hereinafter) is used as each phase shifter. The phase shift amounts of feeding phases are set by ON/OFF-operating the respective bits of the phase shifters. As switches for the respective bits of the phase shifters, semiconductor devices such as PIN diodes or GaAs FETs are used.
The phase shifters are controlled by a control unit. This control unit is connected to each phase shifter through a driving circuit therefor. The control unit and the respective driving circuits are externally mounted on a substrate on which the radiating elements and the phase shifters are formed.
The control unit calculates the optimal phase shift amounts for the orientation of a radiant beam in a desired direction in units of radiating elements, and outputs the corresponding control signals. The driving circuits turn on/off the respective bits of the phase shifters on the basis of the control signals from the control unit.
To increase the gain of the phased-array antenna apparatus, the number of radiating elements may be increased. An increase in the number of radiating elements, however, will increase the number of phase shifters. As a result, many switches to be arranged for the respective bits of the phase shifters are required.
In a conventional phased-array antenna apparatus, modularized semiconductor devices are used as the switches of phase shifters. It takes much time and labor to mount modularized switches on the phase shifters. For this reason, the manufacturing cost of a high-gain phased-array antenna apparatus requiring many switches becomes high.
In addition, if the number of radiating elements is increased to increase the gain of the phased-array antenna apparatus, a large number of driving circuits are required for the respective phase shifters.
In a conventional phased-array antenna apparatus, modularized ICs (to be referred to as phase shifter driving ICs hereinafter) are used as driving circuits for phase shifters. For this reason, a large number of phase shifter driving ICs are required to implement a high-gain phased-array antenna apparatus. A large space is therefore required to allow a large number of IC modules to be externally mounted, resulting in an increase in the size of the phased-array antenna apparatus.
Furthermore, as the numbers of phase shifters and phase shifter driving ICs increase, the number of wiring lines for connecting the phase shifters to the phase shifter driving IC in units of bits increases. However, the number of wiring lines which can be formed within a limited area is limited. For this reason, a high-gain phased-array antenna apparatus has been realized with difficulty in forming wiring lines for controlling phase shifters.